In multi-color electrophotographic imaging systems, latent images are formed in an imaging region of a moving photoconductor (e.g., an organic photoreceptor) belt. Each of the latent images is representative of one of a plurality of different color separation images. The color separation images together define an overall multi-color image. The color separation images may define, for example, yellow, magenta, cyan, and black components that, upon subtractive combination on output media, produce a representation of the multi-color image.
Each of the latent images is formed by scanning a modulated laser beam across the moving photoconductor to selectively discharge the photoconductor in an image-wise pattern. Appropriate liquid color developers (i.e., toners) are applied to the photoconductor after each latent image is formed to develop the latent images. The resulting color separation images ultimately are transferred to the output media or substrate to form the multi-color image.
In some electrophotographic imaging systems, the latent images are formed and developed on top of one another in a common imaging region of the photoconductor. The latent images can be formed and developed in multiple passes of the photoconductor around a continuous transport path (i.e., a multi-pass system). Alternatively, the latent images can be formed and developed in a single pass of the photoconductor around the continuous transport path. A single-pass system enables the multi-color images to be assembled at extremely high speeds relative to the multi-pass pass system. An example of an electrophotographic imaging system configured to assemble a multi-color image in a single pass of a photoconductor is disclosed in co-pending U.S. patent application Ser. No. 08/537,296 to Kellie et al., filed Sep. 29, 1995, and entitled "Method and Apparatus For Producing A Multi-Colored Image In An Electrophotographic System". At each color development station, liquid color developers are applied to the photoconductor belt, for example, by electrically biased rotating developer rolls. The colored liquid developer (or toner) is made of small colored pigment particles dispersed in an insulating liquid (i.e., a carrier liquid).
Excess carrier liquid deposited on the photoconductor belt may stain and smudge the image, and/or cause problems in transferring the image to the transfer roll or output substrate. As such, a liquid removal mechanism such as a squeegee roll may be used immediately after each developer roll to remove excess carrier liquid deposited on the photoconductor belt at each color station. However, before the developed image is transferred to an output substrate, further drying of the image is typically required to remove all (or most all of) any remaining carrier liquid.
Most carrier liquid removal systems or heat based drying systems generate solvent vapors which could be harmful and/or create odors if allowed to be released from the imaging system. As carrier liquid is removed from the photoconductor belt, corresponding solvent vapors must be kept from escaping out of the printer into the ambient air. Separate recovery systems must be used to recover and recycle the solvent in a liquid form. Additionally, most electrophotographic imaging systems include filter systems (e.g., carbon filters) capable of recovery of small amounts of the solvent vapor.
U.S. Pat. No. 5,420,675 to Thompson et al. teaches a drying system that uses a film forming drying roll. The drying roll is in contact with the imaged side of the photoconductor belt. The film forming drying roll has a thin, outer layer which is carrier liquid-phillic and an inner layer which is carrier liquid-phobic and compliant. As the drying roller contacts the photoconductor during the electrophotographic process, the carrier liquid entrains in the carrier liquid-phillic layer and is later removed from it by heating the liquid to a temperature greater than the flash point of the carrier liquid.
U.S. Pat. No. 5,552,869 to Schilli et al. discloses a drying method and apparatus for electrophotography using liquid toners. The drying apparatus removes excess carrier liquid from an image produced by liquid electrophotography on a moving photoreceptor belt. The system includes a drying roll that contacts the photoconductor, with an outer layer that absorbs and desorbes the carrier liquid and an inner layer having a Shore A hardness of 10 to 60 which is carrier liquid-phobic, and a heating means to increase the temperature of the drying roll to no more than 5.degree. Celsius below the flash point of the carrier liquid. In one embodiment, the heating means includes two hot rolls and the system further includes a cooling means which cools the drying roll.
For each of the aforementioned patent references, a separate carrier liquid (i.e., solvent) recovery system is required to remove carrier liquid vapor from the air as it is released during the drying process. As such, a separate carrier liquid recovery condenser unit must be installed adjacent to the drying system.